The present invention relates to a method and a device for automatic estimation of an unwanted pitch moment of an aircraft, in particular a transport aircraft, and also a method and a system for controlling the pitch of an aircraft performing automatic compensation for such an unwanted pitch moment.
It is known that on an aircraft with electrical flight controls, the aircraft is controlled in flight by a pilot, in a manual flight mode, using control members, namely the control stick (in particular a mini-stick), the rudder bar and the thrust control lever. The flight computer(s) interpret(s) the actions of the pilot on these control members and produce corresponding commands which are then sent to control surface actuators (ailerons, spoilers, elevators, etc.) of the aircraft to control the deflection of these control surfaces and thus the aircraft's flight.
With regard to the pitch axis of the aircraft, particularly for a short-term command (of the order of a few seconds, and generally less than ten seconds) made by the pilot of the aircraft, the flight control computers calculate elevator deflection commands, using for that purpose, in general, a standard mathematical law known as C*, detailed below.
However, the pitching movement of the aircraft in flight can be disrupted by (short term) moments that are unwanted, such as:                a pitch moment produced by the extension and retraction of movable surfaces on the main wing of the aircraft;        a pitch moment produced by the extension and retraction of the aircraft's flaps;        pitch moments resulting from transient aerodynamic effects: effects related to the Mach below and above given angles of attack and effects related to the presence of ice on the wing; and        a pitch moment produced by a variation in thrust.        
Within the scope of the present invention, the term “unwanted pitch moments” is used to describe pitch moments of the aircraft as described above, which are produced in the short term (of the order of a few seconds), which have disruptive effects as detailed below, which are not produced by an action by the pilot on the control stick (mini-stick) and which are not wanted.
These unwanted moments can impair the performance of the aircraft, when it is controlled by the C* law alone. They can also have an adverse effect on the comfort of the pilot and the passengers.